The present invention relates to methods of reducing vibration, to active hydraulic anti-vibration mounts and to vehicles including such mounts, these mounts being intended particularly for mounting motor vehicle engines and producing counter-vibrations aiming to neutralize the effects of the vibration of these engines.
More particularly, the invention concerns a method of damping vibration between two rigid elements by interposing between these elements an active hydraulic anti-vibration mount comprising:
first and second rigid support elements integral respectively with the two rigid elements to be connected,
an elastomer body connecting the two support elements and partially delimiting a working chamber filled with a certain volume of liquid,
a flexible wall partially delimiting a compensation chamber filled with liquid, which chamber is linked to the working chamber by a throttled passage also filled with liquid,
a rigid partition integral with the second support element and interposed between the working chamber and the compensation chamber, this rigid partition including a first regulating nozzle,
an exciting device which closes (directly or not) the first regulating nozzle of the rigid partition, this exciting device having a first face communicating with the liquid contained in the working chamber and a second face isolated from said working chamber, said exciting device being so mounted as to be movable perpendicularly to the rigid partition,
a method by which the exciting device is caused to vibrate, creating variations in the volume of the working chamber with a first amplitude xcex94V in order to generate counter-vibrations.
This known method has the disadvantage that when the exciting device is so activated as to be blocked in a position against a stop, which generally happens while the vehicle is moving, vibrations of relatively high frequency and relatively low amplitude (for example, vibrations with a frequency greater than 20 Hz and an amplitude less than 1 mm) are largely transmitted between the first and second support elements of the anti-vibration mount.
Indeed, the throttled passage connecting the working chamber to the compensation chamber is so dimensioned as to damp the effect of vibration movements of relatively low-frequency (for example, below 20 Hz) and of relatively large amplitude (for example, above 1 mm), but it behaves to a considerable extent as a closed conduit with regard to high-frequency vibrations.
The primary objective of the present invention is to mitigate this disadvantage.
To this end, in the method of the type according to the invention, an anti-vibration mount is used in which the rigid partition is traversed by a second regulating nozzle which is closed by a valve device freely movable perpendicularly to the rigid partition, this valve device having a first face in contact with the liquid contained in the working chamber and a second face isolated from the working chamber, the movements of said valve device being limited by first and second stop devices so as to permit variations in the volume of the working chamber limited to a second amplitude xcex4v such that the relationship xcex4v/xcex94V is less than 20% at least while the exciting device is being vibrated.
As a result of these arrangements a decoupling is achieved by which the dynamic stiffness of the anti-vibration mount at high frequencies is reduced when the exciting device is not activated, especially while the vehicle is moving. This decoupling is achieved without impairing the generation of counter-vibrations in the working chamber by the exciting device, since the amplitude of the variations in the volume of the working chamber due to the valve is much less than the amplitude of the variations in volume due to the exciting device when said exciting device is displaced in alternating motions to generate counter-vibrations (generally when the vehicle engine is idling).
In preferred modes of realizing the method according to the invention one and/or the other of the following arrangements can additionally be used if appropriate:
the exciting device is movable at least between a rest position and a blocked position, the second amplitude xcex4v having a first value while the exciting device is in a first range of positions relatively distant from its blocked position and a second value when the exciting device is in its blocked position, the first value being lower than the second value:
the first value equals 0;
the second amplitude xcex4v is constant (in other words, the valve device oscillates between two fixed stops).
In addition, the invention also has the objective of providing an active hydraulic anti-vibration mount for implementing a method as defined above, this mount being intended to be interposed between two rigid elements, and comprising:
first and second rigid support elements intended to be integrated respectively with the two rigid elements to be connected,
an elastomer body connecting the two support elements and partially delimiting a working chamber filled with liquid,
a flexible wall partially delimiting a compensation chamber filled with liquid, which chamber is linked to the working chamber by a throttled passage also filled with liquid,
a rigid partition integral with the second support element and interposed between the working chamber and the compensation chamber, this rigid partition including a first regulating nozzle,
an exciting device which closes the first regulating nozzle of the rigid partition, this exciting device having a first face communicating with the liquid contained in the working chamber and a second face isolated from said working chamber, said exciting device being so mounted as to be movable perpendicularly to the rigid partition at least between a rest position and a blocked position,
and a control link able to link the exciting device to a control device in order to control the movements of the exciting device,
characterized in that the rigid partition is penetrated by a second regulating nozzle which is closed by a valve device movable perpendicularly to the rigid partition, this valve device having a first face in contact with the liquid contained in the working chamber and a second face isolated from the working chamber, the movements of said valve device being limited by first and second stop devices,
in that the second stop device is itself movable perpendicularly to the rigid partition between, firstly, a rest position where said second stop device rests against the valve device in order to lock this valve device against the first stop device, and, secondly, an active position where said second stop device is further away from the first stop device and allows the valve device a certain amount of free play,
in that the second stop device is elastically loaded towards its rest position, and in that the second stop device is linked to the exciting device by means of a mechanical link with lost motion which is able to:
permit said second stop device to remain in its rest position while the exciting device is in a first range of positions relatively distant from its stop position,
displace said second stop device towards its active position when the exciting device is in a second range of positions close to its blocked position,
and maintain the second stop device in its active position when the exciting device is in its blocked position.
In preferred embodiments of the anti-vibration mount according to the invention one and or another of the following arrangements can also be used if appropriate:
the second face of the exciting device communicates with a sealed pneumatic chamber which includes a connection able to be connected to an external pneumatic source;
the exciting device is a flexible membrane linked in a sealed manner to a housing and delimiting with it said pneumatic chamber;
the housing of the pneumatic chamber is contained in the compensation chamber;
the flexible membrane is made of elastomer and includes a peripheral bead which projects from the housing of the pneumatic chamber towards the rigid partition and elastically urges the second stop device towards its rest position, said bead being elastically compressible under the pressure of the second stop device when said second stop device is displaced from its rest position to its active position;
the flexible membrane is reinforced by a central reinforcing element which includes hooking fingers extending towards the rigid partition, said hooking fingers engaging with free play on the second stop device when the flexible membrane is in its first range of positions, and said hooking fingers including hooks which come to rest against the second stop device to pull this second stop device towards its active position when the flexible membrane is in its second range of positions;
the hooking fingers are clipped to the second stop device;
the first nozzle is delimited by a tubular duct extending perpendicularly to the rigid wall between a first end which opens in the working chamber and a second end which communicates with the exciting device, this tubular duct being rigid with the second stop device;
the exciting device is a flexible membrane connected in a sealed manner to a casing and delimiting with said casing said pneumatic chamber;
the flexible membrane is reinforced by a central reinforcing element which includes fitting fingers extending towards the rigid wall, said hooking fingers including hooks which are adapted to come into abutment with a flange which is unitary with the tubular duct for driving the second stop device towards its active position when the flexible membrane is in its second range of positions;
the casing is constituted by a cover which has a bottom and a peripheral wall fixed to the second support element, the pneumatic chamber being delimited between the flexible membrane and the bottom of the cover, and the compensation chamber being situated close to the rigid wall in an inner space delimited between said rigid wall and said cover;
the first nozzle communicates with an intermediate hydraulic chamber full of liquid, which is delimited between the flexible membrane and a rigid ring fixed inside the cover;
the rigid ring has a first annular ring, rigidly fixed to the cover and a second annular rim fitted with a compressible elastomer sealing lip which bears in sealing elastic contact against the second stop device;
the second face of the valve device communicates with the compensation chamber;
the second regulating nozzle has an annular form and is arranged around the first regulating nozzle, the valve device forming a ring arranged inside the second regulating nozzle between the first and second stop devices;
the first face of the exciting device communicates with the working chamber by means of an additional throttled passage which is so dimensioned as to present a resonance frequency between 10 and 90 Hz;
the additional throttled passage is delimited between a fixed wall integral with the rigid partition and a rigid plate forming the second stop device;
the elastomer body has a bell-shaped lateral wall extending along a central axis between firstly an apex integral with the first support element, and secondly an annular base integral with the second support element and with the rigid partition, the apex of the elastomer body being hollowed on each side of the first support element at least in a radial direction, so that said apex forms a shear plug of lower stiffness than said lateral wall in said radial direction;
an intermediate rigid reinforcing element is embedded in the elastomer body between the shear plug and the lateral wall, this intermediate reinforcing element surrounding the shear plug and limiting the radial deflections of the first support element.
In addition, a further objective of the invention is a motor vehicle comprising:
a body,
an engine mounted on the body by at least one hydraulic anti-vibration mount as defined above, in which the second face of the exciting device communicates with a pneumatic chamber,
and a partial vacuum source connected to the pneumatic chamber by means of a control device which is able to:
cyclically vary a gas pressure obtaining inside the pneumatic chamber so as to cause counter-vibrations to be generated in the working chamber by the exciting device when the vehicle engine is idling,
and create a permanent partial vacuum in the pneumatic chamber when the vehicle engine is running at a speed faster than idling speed, thus maintaining the exciting device in its stopped position.
Finally, a further objective of the invention is a motor vehicle comprising:
a body,
an engine,
at least one hydraulic anti-vibration mount for implementing a method as defined above, this mount comprising:
first and second rigid support elements one of which is integrated with the engine and the other with the body,
an elastomer body connecting the two support elements and partially delimiting a working chamber filled with a certain volume of liquid,
a flexible wall partially delimiting a compensation chamber filled with liquid, which chamber is linked to the working chamber by a throttled passage also filled with liquid,
a rigid partition integral with the second support element and interposed between the working chamber and the compensation chamber, this rigid partition including a first regulating nozzle,
an exciting device which closes the first regulating nozzle of the rigid partition, this exciting device having a first face communicating with the liquid contained in the working chamber and a second face communicating with a pneumatic chamber, said exciting device being so mounted as to be movable perpendicularly to the rigid partition between a rest position and a blocked position,
and a partial vacuum source connected to the pneumatic chamber by means of a control device which is able to:
cyclically vary a gas pressure obtaining inside the pneumatic chamber in order to cause the exciting device to vibrate, creating variations in the volume of the working chamber having a first amplitude xcex94V in order to generate counter-vibrations, when the vehicle engine is running at idling speed,
and create a permanent partial vacuum in the pneumatic chamber when the vehicle engine is running at a speed above idling speed, thus maintaining the exciting device in its blocked position, characterized in that the rigid partition is penetrated by a second regulating nozzle which is closed by a valve device freely movable perpendicularly to the rigid partition, this valve device having a first face in contact with the liquid contained in the working chamber and a second face isolated from the working chamber, the movements of said valve device being limited by first and second stop devices so as to permit variations in the volume of the working chamber limited to a second constant amplitude xcex4v such that the relationship xcex4v/xcex94V is less than 20%.